The present invention relates generally to accumulator nozzle fuel injection systems and relates more particularly to a new and improved accumulator nozzle fuel injection system providing improved control of both the fuel injection rate and the volume of the injected charge.
It is a principal aim of the present invention to provide a new and improved accumulator nozzle fuel injection system for controlling the rate of fuel injection throughout the full speed and load range of the associated internal combustion engine to provide increased engine efficiency, reduced combustion pollutants or an optimum compromise of engine efficiency and reduced pollutants at all operating conditions of the engine. In accordance with the present invention, an accumulator nozzle fuel injection method and apparatus is provided for varying both the accumulator pressure and the injection interval for establishing the rate of fuel injection and the volume of the injected fuel charge. More specifically, throughout the full speed and load operating range of the associated internal combustion engine, the accumulator pressure is controlled to control the rate of fuel injection and both the fuel injection interval and accumulator pressure are controlled to establish the volume of the injected fuel charge.
It is another aim of the present invention to provide a new and improved accumulator nozzle fuel injection method and apparatus for terminating the fuel injection event quickly and cleanly and thereby avoid undesirable end of injection fuel dribble or fuel throttling which reduces combustion efficiency and increases combustion pollutants.
It is another aim of the present invention to provide a new and improved accumulator nozzle fuel injection method and apparatus of the type disclosed in the German application No. 26 47 744 in such a manner that the injection of fuel can be more exactly controlled with regard to the rate of fuel injection and the quantity of fuel injected so that the fuel combustion efficiency is improved and the emission of toxic constituents in the exhaust gas is reduced.
The fuel injection method and apparatus of the present invention is primarily useful with a diesel engine and therefore a diesel engine incorporating an embodiment of the fuel injection system of the present invention is disclosed herein. The disclosed system comprises a common fuel plenum or supply chamber for supplying fuel continuously at a regulated pressure to each of a plurality of fuel injectors of the diesel engine. Fuel is continuously supplied to the common supply chamber by a continuously operating fuel pump. A pressure regulator is provided for the supply chamber for regulating the supply pressure and the supply chamber is directly connected via a fuel inlet manifold to each of the fuel injectors. Each fuel injector has a first fuel storage or accumulator chamber for accumulating fuel at the supply pressure for subsequent injection of fuel when an injection valve needle of the injector is momentarily lifted from its seat. A second fuel control chamber is provided within each fuel injector, connected by a passage constriction or orifice to the fuel inlet of the injector, to provide a closing hydraulic bias at the fuel inlet pressure on the injection valve needle. A solenoid pilot valve is momentarily energized for a selected short interval determined by the width of its operating pulse to momentarily reduce the control chamber pressure to trigger the fuel injection event.
The objects of the fuel injection method and apparatus of the present invention are accomplished through the provision of (a) an accumulator chamber having a volume which is substantially larger than the maximum volume of fuel to be injected throughout the full speed and load range of the associated engine and (b) an accumulator inlet constriction or orifice for restricting the inlet flow rate to the accumulator chamber during the fuel injection event to substantially less than the injection rate. As a result, a quantity of fuel is precompressed in the accumulator chamber adjacent the injection valve opening for subsequent injection without moving a relatively long column of liquid. The volume of the accumulator chamber and the throttling action of the accumulator inlet constriction are selected to obtain the desired relationship between the accumulator pressure drop and the injected volume for accurately controlling both the injection rate and volume and for quickly terminating the fuel injection event without undesirable end of injection fuel dribble or fuel throttling. Also, just as the control chamber is isolated by the first passage constriction, the accumulator chamber is isolated by the second passage constriction and thereby protected from any pressure surge or pressure wave in the inlet pressure manifold which might otherwise adversely affect the precise control of the fuel injection event.
Other objects will be in part obvious and in part pointed out more in detail hereinafter.
A better understanding of the present invention will be obtained from the following detailed description and the accompanying drawings of an illustrative application of the invention.